1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus and an image reading system and, more particularly, to one-dimensional and two-dimensional photoelectric conversion apparatuses each for reading an image, for example, of video cameras, digital cameras, facsimile machines, image scanners, digital copiers, X-ray image pickup apparatus, or the like, one-dimensional photoelectric conversion apparatus having a resolution switch function of switching between resolutions in the main scanning direction, and an image reading system having a resolution control means.
2. Related Background Art
In these years, equal-magnification contact type image sensors equipped with multiple semiconductor photosensor chips have actively been developed as one-dimensional image reading apparatus in the field of information processing systems.
For example, Japanese Patent Application Laid-Open No. 5-227362 suggests the contact type image sensor provided with a novel control terminal for control of resolution and permitting a user to switch between resolutions according to use conditions.
FIG. 1 shows a circuit diagram of an integrated circuit for the contact type image sensor suggested in the above application. In the prior art, the resolution switching between a high resolution mode and a low resolution mode is implemented by providing an image sensor chip with a control terminal 125 and allowing the user to enter a signal of a high level or a low level into the terminal.
The prior art, however, had the problem of incapability of achieving sufficient sensitivity and reading speed in the low resolution mode, because light-receiving elements (photodetectors) were arrayed at the pitch of the maximum resolution in the main scanning direction and in the sub-scanning direction.
For example, let us consider an example in which the photodetectors are arranged in the optical resolution of 600 dpi and in which the resolutions are 600 dpi in the high resolution mode and 300 dpi in the low resolution mode. In the prior art the resolutions are controlled by thinning-out a pixel only in the main scanning direction. Since the photodetectors are arranged in the resolution of 600 dpi in the sub-scanning direction, where scanning is conducted in the resolution of 300 dpi in the sub-scanning direction, the photoreceptive region used is only half of the effective photoreceptive region, thus leaving a useless area in the photoreceptive region. Therefore, the apparatus is unable to exhibit sufficient performance in the low resolution mode.
Specifically, supposing a certain 600 dpi-spec photoelectric conversion apparatus should require the storage time of 8 msec per line, a 300 dpi-spec photoelectric conversion apparatus having like charge detection sensitivity would have the photoreceptive area of four times that of the 600 dpi-spec apparatus (two times in the main scanning directionxc3x97two times in the sub-scanning direction). Thus the storage time per line of the 300 dpi-spec apparatus could be a quarter of that of the 600 dpi-spec apparatus; that is, the storage time per line of the 300 dpi-spec apparatus could be 2 msec.
In the case of the resolution switching by the prior art, however, because the photoreceptive area in the resolution of 300 dpi is double that in the resolution of 600 dpi even under the assumption that photocarriers in adjacent pixels can be added up, the storage time is half of that in the resolution of 600 dpi, i.e., 4 msec.
Further, since the above storage time per line is one of factors governing the read time in the photoelectric conversion apparatus constructed to perform signal reading operation during the storage period of light signal, for example, as suggested in Japanese Patent Application Laid-Open No. 9-205588, there arises a problem that the reading speed in the low resolution mode cannot be increased fully, in the photoelectric conversion apparatus with the resolution switching function according to the prior art.
An object of the present invention is to provide a photoelectric conversion apparatus and an image reading system permitting optional setting of resolutions in the main scanning direction and in the sub-scanning direction and also permitting attainment of higher reading speed in the low resolution mode.
In order to accomplish the above problem, according to aspect of the present invention, there is provided a photoelectric conversion apparatus comprising photoelectric conversion means comprising a plurality of photodetectors arrayed in a main scanning direction and in a sub-scanning direction, and resolution switch means for effecting switching between resolutions by selecting signals to be read from the plurality of light-receiving elements arrayed in the main scanning direction and in the sub-scanning direction.
According to another aspect of the present invention, there is also provided a photoelectric conversion apparatus comprising a plurality of photodetectors arrayed in a main scanning direction and in a sub-scanning direction, and control means for selecting a signal to be read from the photodetectors arrayed in the sub-scanning direction, in accordance with a resolution in the main scanning direction.
Further, according to another aspect of the present invention, there is provided an image reading system comprising the photoelectric conversion apparatus as described above, driving means for driving the photoelectric conversion means according to a resolution changeover signal, and processing means for processing output signals from the photoelectric conversion means.
The other objects and features of the present invention will become apparent in the description of embodiments which follows.